The present invention is related to a pre-rupture prediction of a structure's load at rupture.
The term structure designates a finished material body, homogeneous or heterogeneous, designed to resist predetermined physical stresses, known here by the term load, which can be both simple or combined. The object of the invention is to predict the endurance limit of the body with respect to the load.
Although the invention can find an application in many types of structures, it will be described herein with reference to its application as regards the inspection of storage tanks for gas under high pressure, and especially as regards the inspection of tanks made of a composite material wound on a metallic liner.
Such tanks, generally spherical, and intended to withstand internal pressures that are capable of reaching or exceeding 800 bars, are subject to non-destructive inspections among which is included inspection by acoustic emissions.
This technique, whose object is to check the well being of the metal and of the composite material, consists of subjecting the tank to be tested to a predetermined pressure stress, which causes irreversible microscopic damages in the materials, the appearance thereof releasing energy in the form of thermal or acoustic energy. Only the acoustic energy, which is easier to use, is detected by means of piezo-electrical sensors and enables any fault in progress to be detected.
Thus, in the course of a test cycle involving incremental pressure up until a maximum predetermined pressure, typically the acoustic emissions are recorded at the design pressure, that is 1.5 times the working pressure of the tank.
An analysis of these acoustic emissions on the basis of pre-established criteria enables one to declare whether the tank is able or unable to fulfill its mission.
It is clear that this technique, although enabling the detection and even the localization of faults in the tested tank, does not provide any indication as regards the effective value of the pressure at rupture, which is necessarily greater than the design pressure.
Up until now, there is no check that can quantify, for each tank, the predictable level of pressure at rupture, which forces one, due to reasons of reliability, to apply safety coefficients that inevitably lead to oversized installations. These oversized installations lead to, especially for structures made of expensive materials, such as the tanks mentioned hereinabove, for aeronautical or space-related use, prohibitive increases in weight and cost.